Optical rangefinder

ABSTRACT

In order to improve target illumination a light emitter comprises several partial light sources ( 3   a   , 3   b   , 3   c   , 3   d ), the partial beams ( 5   a   , 5   b   , 5   c   , 5   d ) of which are collected by means of a beam collector optic ( 2 ) and directed to the aperture of a collimator ( 1 ). The beam collector optic ( 2 ) comprises two half-mirrored sheets ( 12   a   , 12   b ), which each direct two similarly polarized partial beams ( 5   a, b;    5   c, d ) side by side onto a polarization cube ( 13 ), where the pairs of partial beams which are polarized perpendicular and orthogonal to each other are overlaid.

FIELD OF THE INVENTION

The invention relates to an optical rangefinder as used, for example, insurveying plots of ground and structures.

PRIOR ART

Optical rangefinders of the generic type have long been known. However,the luminance of the usually used emitters having a laser diode as alight source is as a rule lower than will be permissible from the pointof view of eye protection. Moreover, the light beam emitted by anindividual laser diode usually has a disadvantageous, very elongatedcross-section, which can lead to insufficient focusing onto the targetand consequently to an inadequate luminous flux and measuring errors.For these reasons, the range and accuracy of measurement and reliabilityof measurement of rangefinders of the generic type will be less thandesirable and in principle also possible.

SUMMARY OF THE INVENTION

It is the object of the invention to provide an optical rangefinder ofthe generic-type whose emitter has a high luminance and ensures goodtarget illumination and high luminous flux at the target.

The advantages achieved by the invention lie in particular in a decisiveimprovement in the range, i.e. in the maximum measured distance or, fora given range, an increase in the accuracy of measurement. Theseadvantages are achieved with a relatively small emitter optical system,which makes it possible to keep the dimensions of the entire devicesmall.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in more detail below with reference tofigures which merely represent the examples.

FIG. 1a shows a diagram of the emitter of a first embodiment of arangefinder according to the invention,

FIG. 1b shows the beam cross-section of the emitter according to thefirst embodiment at the target,

FIG. 2a shows a diagram of the emitter of a second embodiment of arangefinder according to the invention,

FIG. 2b shows the beam cross-section of the emitter according to thesecond embodiment at the target,

FIG. 3 shows a diagram of the emitter of a third embodiment of arangefinder according to the invention,

FIG. 4 shows a diagram of the emitter of a fourth embodiment of arangefinder according to the invention,

FIG. 5 schematically shows the design of the emitter of a fifthembodiment of a rangefinder according to the invention and

FIG. 6 shows the aperture of the collimator of the fifth embodiment ofthe rangefinder according to the invention and the beam cross-section atsaid collimator.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An optical rangefinder according to the invention has an emitter and areceiver which, for example, may be composed in a known manner of anoptical system and avalanche photodiodes as well as an electroniccontrol and evaluation unit, likewise of known design, which controlsthe emission of light pulses by the emitter and evaluates the outputsignal of the receiver which receives the reflected light pulses. Thedistance measurement can be effected by transit time measurement or bythe phase comparison method. Here, “light” is always to be understood asmeaning that it is not limited to the visible range of the spectrum butalso includes at least the infrared range.

The emitter of a rangefinder according to the invention may have largedifferences in its basic design. In every case, however, it has (FIGS.1-5) a collimator 1 and a light source arranged before said collimatorand consisting in each case of at least two partial light sources, aswell as a beam-collecting optical system 2 arranged in the beam pathbetween the light source and the collimator. Each partial light sourcecontains a laser diode, which is usually an edge emitter, or a pluralityof such laser diodes arranged in succession in the direction of theemission edges. The wavelength common to all laser diodes is theinfrared range, preferably from 850 nm to 980 nm, or 1550 nm. Thecross-section of the light beam emitted by a laser diode can in eachcase be reduced parallel to the emission edge and increased transversethereto by superposition by means of a beam-forming optical systemarranged very close to the emission edge and based on light diffractionor refraction, and the light beam can thus be more highly focused.

With wavelengths from 850 nm to 980 nm, the beam can be focused to avery narrow beam, which permits distance gradation with high lateralresolution. Wavelengths of about 1550 nm are also very advantageousbecause the upper limit of the permissible individual pulse energy ofabout 8 mJ, which is determined by eye safety, is a factor of about16000 higher than at wavelengths from 630 nm to 980 nm. The at leastpartial use of this factor, which is possible according to theinvention, permits a very substantial increase in the range or—at agiven range—in the accuracy of measurement.

According to the first diagram (FIG. 1a), the light source consists oftwo partial light sources 3 a,b arranged directly side by side. Thebeam-collecting optical system 2 is in the form of a collecting opticalsystem 4 which is common to both partial light sources and collectspartial beams 5 a,b emitted by said partial light sources in the objectplane 6 of the collimator 1. They enter the aperture of the collimator 1in such a way that each individual partial beam 5 a,b substantiallyfills the aperture and therefore their cross-sections substantiallyoverlap there. At the collimator 1, the partial beams 5 a,b then divergeagain, but only to such an extent that their cross-sections lie directlyside by side at the target (FIG. 1b). The light beam emitted by theemitter has, at the target, a luminous flux which is approximately twiceas great as that of a light beam emitted by an individual laser diode.

According to the second diagram (FIG. 2a), the partial light sources 3a,b are further apart. A separate collecting optical system 4 a;b whichonce again collects the partial beam 5 a or 5 b emitted by it in theobject plane 6 of the collimator 1 is coordinated with each partiallight source. The partial beams 5 a,b are incident side by side on theaperture of the collimator 1, in such a way that they substantiallycompletely fill said aperture and then form a parallel light beam ofcircular cross-section at the collimator 1 (FIG. 2b), which thereforehas, at the target, not only approximately twice as high a luminous fluxas a light beam emitted by individual laser diode, but also a moreadvantageous cross-section.

According to the third diagram (FIG. 3), the partial light sources 3 a,bare arranged opposite one another, and the beam-collecting opticalsystem 2 has collecting optical systems 4 a;b arranged after saidpartial light sources, as well as a prism 7 arranged between saidoptical systems and in the form of a diverter element. The prism 7 hastwo reflection surfaces 8 a,b which divert the partial light beams 5 a,bemitted by the partial light sources 3 a,b into a further, commoncollecting optical system 9 which collects them, in a manner similar tothe light source according to the first diagram, in the object plane 6of the collimator 1 and directs them to its aperture, where theysubstantially overlap. The beam cross-section corresponds to FIG. 1b.The use of a diverter element makes it possible to arrange the partiallight sources 3 a,b relatively far apart, which facilitates the coolingof the laser diodes.

The fourth diagram (FIG. 4) corresponds substantially to the third one.The difference is in particular in the fact that the collecting opticalsystems 4 a,b, 9 are adjusted differently, in such a way that, similarlyto the light source according to the second diagram, there is virtuallyno overlap of the partial light beams 5 a,b, but the aperture of thecollimator 1 is filled by the partial beams 5 a,b incident on it side byside, and they then propagate at said collimator substantially parallelin such a way that the beam cross-section corresponds to FIG. 2b.

FIG. 5 shows, likewise schematically but in more detail, the structureof the emitter of a rangefinder according to the invention, whichcorresponds to a further diagram. In addition to a collimator 1 and abeam-collecting optical system 2, it contains partial light sources 3a,b, which emit partial beams 5 a,b of the same polarity which areoriented perpendicular to one another, and two further partial lightsources 3 c,d, which likewise emit partial beams 5 c,d which areoriented perpendicular to one another and whose polarization isorthogonal to that of the partial beams 5 a,b. The partial light sources3 a,b,c,d consist in each case of a laser diode 10 and a cylindricallens 11 arranged a small distance away from said laser diode. Acollecting optical system 4 a;b;c,d is arranged after each of thepartial light sources 3 a,b,c,d.

A plate 12 a which is half-mirrored and half-transparent so that ittransmits the partial beam 5 a but diverts the partial beam 5 b in adirection parallel to the partial beam 5 a is arranged, as a firstdiverter element, after the collecting optical systems 4 a,b. The seconddiverter element arranged after the collecting optical system 4 c,d is,like the first diverter element, in the form of a half-mirrored andhalf-transparent plate 12 b which transmits the partial beam 5 c whileit diverts the partial beam 5 d in a direction parallel to said partialbeam 5 c. The partial beams 5 a,b on the one hand and 5 c,d on the otherhand each reach, directly side by side, a polarization cube 13, wherethe pairs of partial beams meet at right angles. The partial beams 5 a,bin each case partially overlap with the partial beams 5 c,d which arepolarized orthogonal to them and are collected by a further collectingoptical system 9 in the object plane 6 of the collimator 1 and directedonto its aperture, which is substantially filled in this way (FIG. 6).In the centre of the cross-shaped light spot is an approximately squarespot of twice the luminance, where in each case two partial beams oforthogonal polarization overlap.

Various modifications of the examples described are possible. Thus, inparticular in the case of diagrams 1 to 4, more than the two partiallight sources shown can be used. The collection of partial beams bydiverter elements can be cascaded for increasing the number of partiallight sources, etc. Finally, it is also possible to use laser diodeshaving wavelengths of, in particular, from 600 nm to 1000 nm and inparticular from 630 nm to 980 nm, which are outside the above-mentionedranges.

List of Reference Numerals

1 Collimator

2 Beam-collecting optical system

3 a,b,c,d Partial light sources

4, 4 a,b,c,d Collecting optical systems

5 a,b,c,d Partial beams

6 Object plane of 1

7 Prism

8 a,b Reflection surfaces

9 Collecting optical system

10 Laser diode

11 Cylindrical lens

12 a,b Plates

13 Polarization cube

What is claimed is:
 1. Optical rangefinder having an emitter whichcomprises a collimator and a light source arranged before saidcollimator, and having a receiver and a control and evaluation unit,said light source comprising a plurality of partial light sources, eachhaving a laser diode and all laser diodes emitting at substantially thesame wavelength, and a beam-collecting optical system which is arrangedafter said partial light sources and collects the partial beams emittedby said partial light sources and directs them into an aperture of saidcollimator wherein the partial beams are directed into the aperture ofthe collimator in such a way that the partial beams overlapsubstantially or slightly and the partial beams propagate substantiallyparallel from said collimator.
 2. Optical rangefinder according to claim1, wherein the wavelength is from 630 nm to 980 nm, in particular from850 nm to 980 nm.
 3. Optical rangefinder according to claim 1, whereinthe wavelength is about 1550 nm.
 4. Optical rangefinder according toclaim 1, wherein the beam-collecting optical system has at least onecollecting optical system arranged in the beam path between saidplurality of partial light sources and said collimator.
 5. Opticalrangefinder according to claim 4, wherein said at least one collectingoptical system is immediately after said plurality of partial lightsources.
 6. Optical rangefinder according to claim 4, wherein said atleast one collecting optical system includes a plurality of collectingoptical systems, a separate one of said collecting optical systemsarranged immediately after each of said plurality of partial lightsources.
 7. Optical rangefinder according to claim 6, wherein saidbeam-collecting optical system has at least one diverter element whichin each case diverts at least one partial beam emitted by one of saidplurality of partial light sources.
 8. Optical rangefinder according toclaim 7, wherein said at least one diverter element is in the form of aprism having a plurality of reflection surfaces.
 9. Optical rangefinderaccording to claim 7, wherein said at least one diverter element is inthe form of an at least partly mirrored plate.
 10. Optical rangefinderaccording to claim 9, wherein said beam-collecting optical system has atleast one superposition element for superposing partial beams ofdifferent, orthogonal polarization.
 11. Optical rangefinder according toclaim 10, wherein said at least one superposition element is in the formof a polarization cube.
 12. Optical rangefinder according to claim 1,wherein said beam-collecting optical system has at least one diverterelement which in each case diverts at least one partial beam emitted byone of said plurality of partial light sources.
 13. Optical rangefinderaccording to claim 12, wherein said at least one diverter element is inthe form of a prism having a plurality of reflection surfaces. 14.Optical rangefinder according to claim 13, wherein said at least onediverter element is in the form of an at least partly mirrored plate.15. Optical rangefinder according to claim 14, wherein saidbeam-collecting optical system has at least one superposition elementfor superposing partial beams of different, orthogonal polarization. 16.Optical rangefinder according to claim 15, wherein said at least onesuperposition element is in the form of a polarization cube.
 17. Opticalrangefinder according to claim 1, wherein said beam-collecting opticalsystem has at least one superposition element for superposing partialbeams of different orthogonal polarization.
 18. Optical rangefinderaccording to claim 17, wherein said at least one superposition elementis in the form of a polarization cube.
 19. The optical rangefinderaccording to claim 8, wherein said at least one diverter element is inthe form of an at least partly mirrored plate.